This article analyzes the causes of workers' multiskill training and, based on a survey of manufacturing plants and workers in Korea, concludes that multiskill capability arises from specific on-the-job training paid for by the firm. I describe various aspects of multiskilled workers and set up a theoretical model in which multiskilled workers are assumed to be more productive than specialized workers for producing a new product but less productive for producing an existing product. The model entails several implications, including a positive cross-sectional correlation between the proportion of multiskilled workers and the growth rate of labor productivity.